1. Field of the Invention
The present invention relates to the technology of optical equipment, and more specifically to the technology of separating beams.
2. Description of the Related Art
Optical equipment such as a microscope etc. uses a dichroic mirror as means for separating beams. A dichroic mirror refers to an optical element having different transmittance (that is, reflectance) depending on the wavelength, and the beams entering the optical element are separated into predetermined beams.
For example, a fluorescent microscope uses a dichroic mirror in separating beams into fluorescence and excitation light. The wavelength of fluorescence tends to be longer than the wavelength of excitation light (referred to as a Stokes' shift). To separate beams by taking the advantage of the characteristic, a dichroic mirror is arranged at the position of coupling the optical path of excitation light (illumination optical system) to the optical path of fluorescence (observation optical system).
However, the wavelength of fluorescence and the wavelength of excitation light depend on the fluorescence substance to be used. In many cases, plural fluorescence substances are combined for use. Therefore, the optimum dichroic mirror is to be selected for each observation performed. To attain this, a number of dichroic mirrors are to be prepared, which means an increasing cost and an upsized and more complicated device. In addition, exchanging dichroic mirrors requires some time, which is the problem in an observation requiring management of time with high accuracy during observation such as a high-speed observation.
Relating to the above-mentioned problem, Japanese Published Patent Application No. 2003-21788 discloses the technology using a non-coated glass (or using a reflection preventive coat to adjust reflectance) instead of a dichroic mirror as means for separating beams. In this method, since normal optical glass including the non-coated glass substantially is wavelength-independent, it is not necessary to exchange means for separating beams for each fluorescence substance.